Tetracyclines are broad-spectrum antibiotic, which are routinely used orally for the treatment of dermatological conditions, such as acne and rosacea. However, despite their high therapeutic value, tetracyclines are very unstable, and they are known to be incompatible with many formulation excipients, including water, various protic substances and oxidizing agents.
Topical tetracycline was the first topical antibiotic approved for the treatment of acne, its use has been limited because of the skin penetration problems of the active ingredient (Adişen E et al, “Topical tetracycline in the treatment of acne vulgaris”, J Drugs Dermatol. 2008; 7:953-5). The vehicle of this product is an ointment base, comprising petrolatum (which is greasy and unusable in the case of facial treatment of acne and rosacea).
Tetracycline hydrophobic compositions intended to be mixed with an external source of protic liquid are known. They comprise a hydrophobic non-hygroscopic silicone thickening agent, preferably a silicone elastomer, in concentrations of more than 5%. This mixing results in substantial solubilization of the tetracycline, thus rendering it “suitable for topical delivery. Such a product, which requires mixing two components prior to administration by the patient is cumbersome and has no or little practical or viable value; and furthermore, it would degrade and form degradation products if left for a while prior to treatment.